> There is currently no comparable rocket system comparable to SLS even with all its warts. If it flies today, it's the only operational Human rated heavy lift system. Starship is promising, but still a lot more speculative.
It's human-rated only because NASA says it is. It has literally never flown. The NASA rules for human-rating its own internal-designed craft are way looser than the rules for human-rating commercial craft. SpaceX and Boeing had to jump through way more hoops to get their platforms human-rated by NASA.
Artemis could just as easily be done by launching Orion + service module, and upper stage to LEO on separate Falcon Heavy launches, then launching crew on Dragon or Starliner. No starship required. It would be 3 launches, but with autonomous LEO rendezvous there would be no risk to the crew, for about 1/10th the cost (or alternatively, 5 missions a year instead of 1 every 2 years).
This, btw, was NASA's plan before congress mandated the use of SLS!
> Using the shuttle systems reduces the engineering risks.
The extensive changes made for SLS and the fact that ~none of the original engineers were involved invalidates all that heritage. Or at least it would if NASA held the SLS program to the same standards as commercial industry.
> This means that SLS may be more expensive than something scratch-designed, but there is also a lot less insecurity in the schedule (though there was enough ...).
SLS has had more budget and timeline overruns than anything else out there. Even SpaceX's famously optimistic "Elon time" is not as bad as SLS's delays.
> I don't think there was a way for NASA to start the Artemis program sooner than with SLS.
Again, this was the plan before congress got in the way. I remember it vividly as I worked at NASA at the time.
> I don't think it's a good idea to entirely depend on SpaceX for heavy lift rockets or human rated space flight.
ULA would be happy to develop a super-heavy Vulcan. Or Rocket Lab. Or Relativity. etc. Do the same as COTS: fully fund two providers, and if one drops out then fund a 3rd.
> I also don't understand your point about Orion not being able to go to the moon.
Orion has insufficient fuel to enter circular LLO (like Apollo) and still get home. It's too heavy and under-powered compared with the Apollo Command and Service Modules.